1. Field of the Invention
The present invention relates to a semiconductor device containing a circuit structured by a thin film transistor (hereafter referred to as a TFT), and to a method of manufacturing thereof. For example, the present invention relates to an electro-optical device, typically a liquid crystal display panel or an EL display panel, and to electronic equipment (electronic instruments) loaded with this type of electro-optical device (electronic device) as a part.
Note that, throughout this specification, the term semiconductor device indicates general devices which function by utilizing semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electronic equipment are all semiconductor devices.
2. Description of the Related Art
Techniques of structuring a thin film transistor (TFT) using a semiconductor thin film (having a thickness on the order of several nm to several hundreds of nm) formed on a substrate having an insulating surface have been in the spotlight in recent years. The thin film transistor is widely applied in electronic devices such as ICs and electro-optical devices, and in particular, its development is accelerating as a switching device of a liquid crystal display panel or an EL display panel.
Amorphous silicon or polysilicon semiconductor TFTs are arranged in a matrix shape in a liquid crystal display panel, and a liquid crystal is maintained between an element substrate, on which pixel electrodes, source lines, and gate lines connected to each TFT are formed, and an opposing substrate having an opposing electrode. Further, a color filter for color display is formed on the opposing substrate. A polarizing plate is arranged as a light shutter in the element substrate and in the opposing substrate, and a color image is displayed.
The color filter of the liquid crystal display panel has R (red), G (green), and B (blue) colored films, and a shading mask left only between pixels, and red color, green color, and blue color light is extracted in accordance with light passing through. Furthermore, the shading mask of the color filter is generally structured by a metallic film or an organic film containing a black pigment. The color filter is formed in a position corresponding to the pixels, and the color of light output can thus be changed for every pixel. Note that the term position corresponding to the pixels indicates a position coinciding with the pixel electrodes.
Note also that, throughout this specification, the term color filter indicates one patterned colored film given a red, green, or blue color.
Further, among EL display devices, there is a colorizing method in which EL elements for emitting light showing a red color, a green color, or a blue color are arranged in a matrix state, and there is a colorizing method in accordance with a color filter used by EL elements which emit white color light. The colorizing method in accordance with a color filter used by EL elements which emit white color light is similar in principal to a colorizing method for a liquid crystal display device which uses a color filter.
With a liquid crystal display panel in which a color filter is formed in the opposing substrate, it is necessary to perform assembly of the element substrate and the opposing substrate with extremely high precision, and when this precision is low, a the aperture ratio is reduced and there is a problem in which the display becomes darker.
Further, with a liquid crystal display panel in which a metallic film is used as a shading mask, a problem develops in which a signal delay easily generates due to a parasitic capacitance with other wirings. Furthermore, when an organic film is used, a problem that the number of process steps increases is caused.
In addition, with an EL display device using an EL element for emitting light showing a red color, a green color, or a blue color, the EL material differs for each color, and therefore the element characteristics also differ, and it becomes difficult to obtain a uniform display. For example, characteristics such as the deterioration speed of the EL material differ for each material, and therefore a problem in which the displays become dispersed due to elapsed time develops.
Furthermore, an EL display device using an EL element which emits white color light is, in principle, similar to a liquid crystal display device using a color filter, and therefore problems similar to those above develop.